An overspecified truth table contains at least one decision that never executes because a previous decision specifies it in the Condition Table. The following example shows the Condition Table of an overspecified truth table.
The decision in column D3 (
-TT) specifies the
TTT. These decisions are duplicates
of decisions D1 (
FTT) and D2
TFT). Therefore, column
D3 is an overspecification.
The following example shows the Condition Table of a truth table that appears to be overspecified, but is not.
In this case, the decision D4 specifies two decisions
FTT also appears
in decision D1, but
TTT is not a duplicate.
Therefore, this Condition Table is not overspecified.
An underspecified truth table lacks one or more possible decisions that require an action to avoid undefined behavior. The following example shows the Condition Table of an underspecified truth table.
Complete coverage of the conditions in the preceding truth table requires a Condition Table with every possible decision:
A possible workaround is to specify an action for all other possible decisions through a
default decision, named
The last decision column is the default decision for the truth table. The default decision covers any remaining decisions not tested in the preceding decision columns. See The Default Decision Column for an example and more complete description of the default decision column for a Condition Table.